This invention pertains to curable polymeric compositions and in particular to novel curable polymeric compositions containing unsaturated hydantoin derivatives.
Some unsaturated hydantoin derivatives are known. British Pat. No. 846,601 pertains to vinyl derivatives of substituted monohydantoins, processes for preparing these materials and to polymers and copolymers containing such moieties. 3-Vinyl and 1,3-divinyl hydantoin derivatives are described. These materials are homopolymerized or copolymerized with other unsaturated polymerizable molecules. The use of the 1,3-divinyl compounds as crosslinking agents in the copolymerization with other unsaturated compounds is disclosed. Unsaturated bis or tris hydantoins are not suggested.
3-Allyl-5,5-dimethylhydantoin is disclosed by M. Sato, Nippon Kagaku Zasshi, 83, 323 (1962); Chem. Abst. 59, 3908 (1963).
A crosslinking agent is a polyfunctional compound which when incorporated into a polymerizing system enters the polymerizing chains, and by virtue of its polyfunctional nature leads to crosslinked or network structures.
In the free radical polymerization systems, polyfunctional vinyl monomers such as divinylbenzene, ethylene bismethacrylate and triallyl cyanurate are well known as crosslinking agents. British Pat. No. 846,601 suggests that 1,3-divinylhydantoins might be such crosslinking agents as well. These crosslinking agents contain active ethylenic double bonds which react with active ethylenic double bonds in the other monomers present to undergo the crosslinking polymerization reaction.
However, it is known that essentially saturated high molecular weight polymers are often subject to deterioration by thermal, oxidative, light, irradiation or chemical means. Among such polymers are the polyolefins such as polyethylene, polypropylene and the like. These polymeric materials are currently being extensively used as insulation for wire and cable, in conduits, in containers, etc. The fabrication, molding, extrusion, and calendering of these materials is readily accomplished by standard methods. Despite all this, however, the applications of these polymers are circumscribed by their lack of high temperature form stability, that is, their inability to retain a particular shape at elevated temperatures, by their solubility in certain solvents, and by their relatively poor resistance to environmental stress cracking. In U.S. Pat. Nos. 3,264,252 and 3,562,202 it is disclosed that the physical properties of such polymers can be greatly improved by the addition thereto of a minor amount of quinone oxime and curing at a temperature above 170.degree. C. The hydrocarbon insolubility of the polymers is improved and the polymers have increased resistance to creep and to stress cracking.
Chlorinated polyethylene elastomers are well known materials in the rubber art. They are prepared from branched or linear polyethylene by homogeneous solution chlorination or by chlorination of dispersions of finely divided polyethylene in water or other suitable dispersing media. Solution chlorination gives a chlorinated polyethylene of relatively uniform distribution of chlorine atoms on the polymer chain, while dispersion chlorination gives products with a more random distribution of chlorine. Using either method, it is well known that the introduction into the polymer molecule of between 20 and 50% chlorine atoms by weight produces an elastomeric product from polyethylenes which are highly crystalline before chlorination.
Useful elastomeric products must necessarily be vulcanized, or cured by cross-linking. Vulcanization of chlorinated polyethylene has generally been difficult, and the products known as chlorosulfonated polyethylenes, which contain a minor proportion of sulfonyl chloride groups as reactive cross-linking sites are often employed in applications where the simple chlorinated polyethylenes might otherwise be preferred. It has been recommended in the art to vulcanize chlorinated polyethylenes with peroxides, for example, in U.S. Pat. No. 2,534,078, but vulcanizates so obtained are difficult to prepare and have not had physical properties adequate for many uses.
In U.S. Pat. No. 3,531,455 the curing of chlorinated polyethylene composition using an organic peroxide and a polyunsaturated coagent triallyl cyanurate is described to give highly vulcanized products with good properties.
It is well known to promote the peroxide vulcanization or curing of saturated chain polymers by including in the formulation any of a variety of polyunsaturated coagents.
Among the coagents disclosed in the prior art are various maleimides such as N,N'-m-phenylene dimaleimide; allyl esters such as diallyl phthalate, diallyl sebacate, diallyl adipate, allyl methacrylate, diallyl itaconate, triallyl aconitate, diallyl carbonate of diethylene glycol and the like; divinylbenzene, triallyl cyanurate, polybutadiene (1,2), triallyl phosphate, triacryloylhexahydrotriazine, and polyfunctional acrylate or methacrylate esters such as ethylene dimethacrylate, butylene dimethacryate, polyethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, ethylene diacrylate and the like.
The essentially saturated polymers which can be cured with the help of coagents include chlorinated polyethylene (A. R. Guy et al. Rubber World, 162(3),60(1970); poly(vinyl chloride) (M. H. Gerard, Soc. Plast. Eng., Tech. Pap., 17, 480 (1971); polypropylene (Japan Patent 71,10664); copolymers of ethylene/vinyl acetate, ethylene/vinyl chloride and ethylene/propylene; chlorosulfonated polyethylene; various rubbers such as nitrile rubber, EPM, EPDM, NBR, SBR and the like.
When peroxide curing is involved, any of the peroxides normally used in curing polymeric systems can be employed. Representative types of peroxides are aryl peroxides, acyl peroxides, aralkyl peroxides, alkyl peroxides and ketone peroxides. Specific examples are dicumyl peroxide and its higher homologues, dibenzoyl peroxide, lauroyl peroxide, succinyl peroxide, methyl ethyl ketone peroxide, n-butyl 4,4'-bis(t-butyl peroxy)valerate, acetyl peroxide, dicamphoryl peroxide, phthalyl peroxide, tertiary butyl hydroperoxide, ethyl percamphorate, hydroxyalkyl hydroperoxides and other similar organic peroxides or substances which give rise to such peroxides under the hereinafter described reaction conditions. Dicumyl peroxide is preferred because of the fast rate of cure and excellent vulcanizate properties which result from its use.
The use of coagents in the radiation curing of polymers for improved properties is also known, (G. R. Berbeco, Insulation/Circuits, 17(2),23(1971)). Radiation processing is carried out by .gamma.-rays from radioisotopes, primarily cobalt-60, or preferably by high-energy electrons from electron accelerators. The same polymers and coagents described under peroxide curing are also used in the radiation curing process. Japan Pat. No. 71,10664 discloses the irradiation curing of polypropylene using the coagent diallyl carbonate of diethylene glycol.